Although he failed when other passengers overpowered him, experts say the scanners would help prevent a repeat by identifying hidden weapons and explosives.

How does the scanner work?

With the best-known model, passengers are flooded with microwaves which are reflected by the body and then analysed to produce a pale image.

A scan – which produces a low humming – takes about six seconds and an analysis can be made in 30 seconds.

How intimate are the pictures?

Security advisor Hans-Detlef Dau (54, Hamburg), who sells the scanner, said: “Unlike with a complete X-ray examination, the rays do not go deeply under the skin. They see only the things which lie over it, so bladed weapons and firearms as well as ceramics.

“Beyond that, they show intimate piercings, catheters and the form of breasts and penises.

But there is still some uncertainty as to how dangerous the machines are, because a scan with microwaves corresponds to 10,000 mobile phone conversations.

Before the ‘naked’ scanners are introduced, the German government wants to eliminate any doubts over health and privacy.

Interior Minister Thomas de Maiziére told BILD: “Studies on terahertz waves tell us that they are harmless to humans. Nevertheless we will examine carefully in 2010 whether body scanners can damage health. We do not use devices with X-rays.

“In addition, there has been substantial progress with the development of body scanners in terms of protecting privacy.

“There are scanners which make foreign objects visible without showing body outlines. One only sees a stickman figure.”

The Minister believes that public acceptance of the scanners will increase. He added: “Scanning would only be necessary in exceptional cases. Therefore the employment of new, fully developed body scanners could have little effect on passengers.”